Measurement of the g factor of ground-state ⁸⁷Sr at the parts-per-million level using co-trapped ultracold atoms

We demonstrate nuclear magnetic resonance of optically trapped ground-state ultracold ⁸⁷Sr atoms. Using a scheme in which a cloud of ultracold ⁸⁷Rb is co-trapped nearby, we improve the determination of the nuclear g factor, g_I, of the ¹S₀ electronic ground state of atomic ⁸⁷Sr by more than two orders of magnitude, reaching precision and accuracy at the parts-per-million level. We achieve similar accuracy in the ratio of relevant g factors between Rb and Sr. This establishes ultracold ⁸⁷Sr as an excellent linear in-vacuum magnetometer. More generally, our work demonstrates how ultracold neutral atoms can be used for the precise determination of highly relevant atomic and nuclear magnetic properties. These results are important for ongoing efforts towards quantum simulation, quantum computation and optical atomic clocks employing ⁸⁷Sr, and other neutral alkaline-earth and alkaline-earth-like atoms.